bug#52200: 29.0.50; image-dired-cmd-create-standard-thumbnail-options

["Peter Münster" <pm@a16n.net>]

And here the same patch for the latest master:

diff --git a/lisp/image/image-dired-external.el b/lisp/image/image-dired-external.el
index 223d881bcf..fcf2e2edb6 100644
--- a/lisp/image/image-dired-external.el
+++ b/lisp/image/image-dired-external.el
@@ -128,15 +128,13 @@ image-dired-cmd-optipng-options
   :link '(url-link "man:optipng(1)"))
 
 (defcustom image-dired-cmd-create-standard-thumbnail-options
-  (append '("-size" "%wx%h" "%f[0]")
-          (unless (or image-dired-cmd-pngcrush-program
-                      image-dired-cmd-pngnq-program)
-            (list
-             "-set" "Thumb::MTime" "%m"
-             "-set" "Thumb::URI" "file://%f"
-             "-set" "Description" "Thumbnail of file://%f"
-             "-set" "Software" (emacs-version)))
-          '("-thumbnail" "%wx%h>" "png:%t"))
+  (let ((opts (list "-size" "%wx%h" "%f[0]"
+                    "-set" "Thumb::MTime" "%m"
+                    "-set" "Thumb::URI" "file://%f"
+                    "-set" "Description" "Thumbnail of file://%f"
+                    "-set" "Software" (emacs-version)
+                    "-thumbnail" "%wx%h>" "png:%t")))
+    (if (executable-find "gm") (cons "convert" opts) opts))
   "Options for creating thumbnails according to the Thumbnail Managing Standard.
 Available format specifiers are the same as in
 `image-dired-cmd-create-thumbnail-options', with %m for file modification time."

-- 
           Peter